Comprehensive characterization of glycerol/ZnO green nanofluids for advances in multifunctional soft material technologies

Abstract

Nanofluids (NFs) are increasingly used in most of the areas of soft condensed matter technologies, especially for heat transfer, energy harvesting, electrical insulation, and in the development of a variety of optoelectronic devices and controllable systems. Nowadays, green nanofluids are of considerable interest to researchers from an environmental safety point of view. Therefore, in this work, green nanofluids having biodegradable glycerol (GLY) as base fluid with homogeneous dispersion of eco-friendly zinc oxide (ZnO) nanoparticles (concentration range 0.01–1.00 wt%) were prepared and comprehensively characterized by employing various advanced techniques for exploring their promising multifunctional properties. The X-ray diffraction study of these GLY/ZnO green nanofluids, which is the first of its kind on nanofluids, confirmed the existence of monodispersed ZnO nanoparticles in the arranged 3D supramolecular structural network of the glycerol fluid. The ZnO nanoparticles having higher suspension stability in the GLY fluid were able to exhibit all the characteristic crystalline diffraction peaks for the concentration ≥ 0.30 wt%, at which the visible range photons absorption became almost saturated. The detailed analysis of the UV–Vis absorbance spectra of these nanofluids with increasing ZnO concentration explained substantial alterations in the electronic transition energy for the lone electron pairs of the hydroxyl oxygen atoms of glycerol molecules and also the valence band electrons of the ZnO nanomaterial. Dielectric and electrical spectra of these nanofluid materials are carried out in the harmonic field of 20 Hz to 1 MHz range, at 25 °C. A small change in the static dielectric permittivity of these GLY/ZnO nanofluids with the increase of ZnO concentration reveals some modifications in the parallel arranged dipolar ordering of the glycerol molecules. The conductivity relaxation process ruled the electrical conductivity of the GLY/ZnO nanofluids, but the low conductivity of these materials confirmed them as potential candidates for electric insulating nanodielectrics. The decreased viscosity and the increased thermal conductivity with some constructive changes in the acoustic parameters of these nanofluids were noted with the increase of ZnO concentration. The experimental results on the structural, optical, dielectric, electrical, and thermophysical properties of the GLY/ZnO nanofluids are technologically appealing and recognize these as innovative multifunctional soft materials.